How do i read a frequency graph?

[Sirsh]

How do i read a frequency graph??

If i have. a time required of 5-9 and a a frequency of 5. how do i find the average? do i do 9-4*6 or 9*5+5*9/5 ?? thanks.

 

[Mark44]

If i have. a time required of 5-9 and a a frequency of 5. how do i find the average? do i do 9-4*6 or 9*5+5*9/5 ?? thanks.

I don't think you have given a clear explanation of what you are given, but I'll do my best to explain what I think you are asking. Also, I don't think that either of the values you gave is correct. 9 - 4*6 = 9 - 24 = -15, which doesn't make any sense. If you meant (9 - 4)*6, that's 5*6 = 30, and I don't see that this number has anything to do with anything. For the other expression, 9*5+5*9/5 = 45 + 9 = 54, but that doesn't have anything to do with anything, either.

I believe that the time required, 5 - 9, means a time interval of 5 to 9 time units of some kind, and the frequency of 5 means that 5 times were between 5 and 9 (sec? min? hours?).

The average time would be (5 + 9)/2 = 7

 

[Sirsh]

Sorry i meant.
|Time required to complete test| Frequency | Midpoint |
| 5-9 | 6 | 7 |
| 10−14 | 12 | 12 |
| 15−19 | 25 | 17 |
| 20−24 | 34 | 22 |
| 25−29 | 16 | 27 |
| 30−34 | 7 | 32 |

What would be the mean of this? sorry.

Would i just do total of (frequency * midpoint)/amount scores?

 

[Mark44]

Something like that. For each category, multiply the frequency by the midpoint of the category. Add all these products and divide by the total frequencies. IOW,
(f₁ * m₁ + f₂ * m₂ + ... + f_n * m_n)/(f₁ + f₂ + ... + f_n)

 

[Sirsh]

Thank you. Do you know how i'd go around getting the stadard deviation? Is it root(x-mean)^2/n?